The USGS in collaboration with the Colorado Geological Survey, is determining the location, thickness, and quality of Front Range aggregate resources.

The two primary sources of aggregate in Colorado are deposits of sand and gravel along rivers or streams, and certain types of bedrock in the foothills or mountains.

Nearly 80 percent of our aggregate is sand and gravel. The thickest deposits of gravel with the highest quality occurs as low terraces (see diagram below). Mining other gravel deposits such as dissected fans or dissected high terraces, commonly requires disturbing more land to obtain the same amount of useful gravel.

About 20 percent of our aggregate is crushed stone. It is quarried in areas where good quality bedrock is near the surface (parts of the brown areas on the diagram). Not all of the bedrock is good enough to be used for cement concrete or asphalt.

  Figure 1.  Colored relief map showing typical topography along the Front Range

Transportation adds greatly to the cost of aggregate. A rule-of-thumb is, if aggregate is shipped 30 miles, transportation will double the cost of the aggregate. Therefore it is important that high quality sources of aggregate, located are near the market area, are identified and protected for future use.

U.S. Department of the Interior, U.S. Geological Survey URL: http://rockyweb.cr.usgs.gov/frontrange/virtour/howepit2.htm Contact: Carol Mladinich  mailto:csmladinich@usgs.gov Updated: 05/16/2001